fix(diff-filter): add build system output dirs + lockfiles (#162)

[Saadat555]

Closes #162

Summary of changes:

1. Added 9 missing build-system output directories to GENERATED_DIR_PREFIXES in packages/diff-filter/src/patterns.ts:

   • obj/ (.NET / C# intermediate build output)
   • zig-out/ (Zig build output)
   • bazel-out/ (Bazel output base)
   • buck-out/ (Buck / Buck2 build output)
   • .stack-work/ (Haskell Stack working directory)
   • dist-newstyle/ (Haskell Cabal new-style build)
   • .lake/ (Lean 4 build directory)
   • elm-stuff/ (Elm build artifacts)
   • nimcache/ (Nim compilation cache)

2. Added 2 missing lockfiles to LOCKFILE_NAMES in packages/diff-filter/src/patterns.ts:

   • stack.yaml.lock (Haskell Stack)
   • paket.lock (F# / .NET Paket)

3. Added comprehensive test cases in packages/diff-filter/tests/classify.test.ts to verify all newly added patterns are correctly identified and ignored.

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